This invention relates to catalysts and, more particularly, to catalysts employed for the steam reforming of hydrocarbons in the manufacture of methane containing gases, for example, Substitute Natural Gas, SNG.
Catalysts comprising nickel and alumina have been known for many years which are useful in the catalytic steam reforming of hydrocarbons. However, over the years considerable development of the catalysts has occurred, particularly to meet and overcome problems imposed by the feedstocks employed in the gasification processes.
In U.K. Patent Specification No. 1,342,020 there is described and claimed a method for preparing catalytic materials containing inter alia a Group VIII metal and alumina, by co-precipitation at a temperature of 50.degree. to 100.degree. C. using an alkali bicarbonate as the precipitating agent.
U.K. Patent Specification No. 1,462,060 described the preparation of catalysts comprising a Group VIII metal, e.g., nickel alumina, by coprecipitation using alkali carbonates as the precipitants.
The preparative routes taught by the prior art involve either adding a solution of the catalytic agents to the precipitant solution or admixing both solutions simultaneously, preferably at a temperature of 80.degree. C. or above.
A general discussion of the art of steam reforming in the manufacture of methane-containing gases and of the problems which have arisen and have been overcome in disclosed in U.S. Pat. No. 4,105,591. This patent also describes catalysts which have improved resistance both to deactivation by polymer formation and to sintering.
Polymer resistance is particularly important when gasifying heavy feedstocks such as kerosine and gas oil.
Hitherto it has been possible to avoid polymer formation with these feedstocks only by employing high preheat or inlet temperatures. The use of such high inlet temperatures leads to high outlet temperatures, with the result that the methane concentration in the product was not as high as it would have been with lower preheat temperatures. The use of high working pressures also tends to increase the outlet temperature.
We have now found that catalysts can be produced which are capable of giving satisfactory performance in the gasification of kerosine with a preheat of 500.degree. C., against preheats of 550.degree. C. and above as required for commercially available catalysts for this feedstock.